The overall project seeks an understanding in detail of the kinetic, chemical, and complete metal ion dependent stereochemical mechanisms utilized by the first enzyme of histidine biosynthesis in Salmonella typhimurium, ATP phosphoribosyltransferase (EC 2.4.2.17), to effect integrated metabolic regulation. We will complete the arginine modification studies. The especially reactive lysis residue in the ATP phosphoribosyltransferase active site provides a method for identifying an active site peptide. We will attempt to covalently label this lysine with pyridoxal phosphate followed by borotritide reduction. Trypsin degradation followed by isolation of the labeled peptide should allow identification of the lysine residue since the amino acid sequence is known. We hope to also synthesize exchange inert COIII complexes of ATP and PRibPP, to determine whether any are substrates for the enzyme, and to separate them into positional and optically pure complexes. COIII complexes which are substrates would be studied by visible CD spectroscopy when bound to the enzyme in the absence and presence of histidine to characterize conformational changes at the active site.